The invention relates to a fibrillation device for the manufacture of mineral wool.
In the manufacture of mineral wool, a stream of molten oxide of suitable composition and viscosity is caused to run down onto one or more rapidly rotating spinning wheels which constitute a fibre-forming device. The stream of melt strikes the first spinning wheel or the narrow gap between the first pair of spinning wheels which rotate in opposite directions. The melt adheres to the peripheral surface and is thereafter, as a result of centrifugal force, thrown out from said surface in the form of fibres of melt. These fibres are cooled down and transported into the wool chamber and to the receiving conveyor with the aid of a stream of air which is blown in just outside the spinning wheel or spinning wheels and partly with the aid of air flowing around the fibrillation device. This air flow is produced by means of a partial vacuum maintained in the suction box under the receiving conveyor and in the wool chamber. The spinning wheels are usually four in number and they rotate preferably pairwise in opposite directions. The bulk of the melt is thrown out from the uppermost spinning wheel onto the following wheel where part of the melt is consumed in forming fibres and the remaining unfibrillated melt is transferred to the respective following wheel, until all the melt introduced has been fibrillated or has departed in the form of beads or slag. The unfibrillated waste beads fall down and are recovered.
The air stream is blown in through a slit which is concentric with the peripheral surface of the spinning wheel and located adjacent thereto along the outwardly facing peripheral surfaces. The air current cools the newly-formed fibres, to which a binder is then added from binder spray nozzles located in the centre of the spinning wheel and/or around the outside and behind the spinning wheels. The air currents transport the stream of fibres from the fibrillation device onto the receiving conveyor, which is perforated and on which the fibres form a thin mat.
Fibrillation devices of this kind are previously known from e.g., U.S. Pat. No. 3,785,791 and the British patent specifications GB 867,299 and 1,559,117.
According to the older British patent, the current of air is blown in through a slit which is located outside and concentric with the peripheral surfaces of the spinning wheels, parallel with the axes of rotation of the spinning wheels.
According to the more recent British patent the air stream which is introduced parallel to the axis is simultaneously given a tangential velocity component in the direction of rotation of the spinning wheel with the aid of inclined guide vanes in the air gap.
In the fibrillation stage, the melt adheres to the peripheral surface of the spinning wheel on which it forms a thin ring of melt which moves from the first spinning wheel to the next spinning wheel at the same time as melt is thrown out in the form of fibres from the respective spinning wheels. The air stream, which has as its purpose to cool the fibres before they encounter the binder and to transport the fibres from the fibrillation zone to the receiving conveyor, meets the newly-formed fibres in a direction which is parallel to the axis of rotation of the spinning wheel but inclined in the direction of rotation as a consequence of the inclined guide vanes in the air gap.
In the fibrillation stage a large part of the fibres is broken as a result of the blowing. It is assumed that at a certain temperature the fibres are extremely brittle and break easily.
Another drawback in connection with fibrillation according to the known processes is that blowing with unheated air causes a cooling down of the ring of melt adhering to the spinning wheel. This has an adverse affect on fibre formation. In addition, the air stream, which besides impinging on the newly-formed fibres also impinges on the melt ring located immediately below, causes a displacement and deformation of the melt ring on the peripheral surface of the spinning wheel, as a consequence of which the fibre-forming situation is more difficult to control.